Watch crystal for watertight watches



Patented Jan. 23, 1940 UNITED STATES 2,187,868 ws'rcn cars-ran roawarn-anon WATC Ernest mm, La Chaux-de-Fonds, swam-nus ApplicationFebruary 8, 1937, Serial No. 124,495 In Switserland May 11, 1936 3Claims.

| water pass into their inside to cause corrosion of the metallic partsor to form a damp vapor which is deposited on the crystal and hindersthe reading of the dial. Such leakage is all due to an inefficient tightjoint between bezel, crystal and 10 case band the water penetratingthrough said joint when the temperature of the interior of the watchcontracts the air therein enclosed.

-'----- Packings;-have-be'en used for overcoming said These packingsmust besomewhat resilient and must therefore have a certain thickness,which determines also the depth of the groove. Now since this groovemust on no account extend into the hole of the winding stem it becomesnecessary to keep the case band somewhat thickened when said packingsare used. g

The object of this invention is a crystal which may be put in withoutthe above-mentioned inconveniences. The invention consists in providinga crystal having atleast partly compressible If the crystal is made, forinstance, of a transparent artificial resin, like that known by the nameof "Ple'xiglass", which is a synthetic resin obtained by apolymerization of lactic acid, the edges of such a crystal, after beingthinned, could be covered with a'molliiled band of the same resin.which, as is known, can be produced with a consistency varying from apasty mass, to an elastic sheet and finally, according to its treatment,to a colourless horny plate which will break only after being bent at avery sharp angle. This bandconsists of a permanently soft syntheticresin material which remains soft at room temperatures. Such a'crystalcan be pressed between besel and case band to form an absolutely tightjoint which will prevent entry of humidity into the watch.

Another manner of proceeding consists in mollifying the edges of thewatch crystal, made of resin, after having given it the desired form.either by a thermal or by a chemical treatment.andinclampingitbetweenthebezelandthecase band so that it forms apermanently soft packing closely applied to said two members. Thissoftened edge remains soft at room temperatures. The annexed drawingshows as examples some embodiments of the invention.

Fig. 1 shows partly in plane square watchcrystal.

Fig. 2 is a sectional view on line lI-II of Fig. 1. Fig. 3 is asectional view on line III-HI of the crystal shown in Fig. 4.

Fig. 4 is a plan view of a circular crystal. Fig. 5 is a sectional viewof a circular watch crystal having edges prepared according to theinvention.

In the crystal according to Figs. 1 and 2 the edges a have been thinned.They have been coated with a layer b of a mass which consists in a smallband of resin having a permanently soft consistencywhich remains so atroom temperatures. when the crystal is clamped against the case bandthis kind of packing is perfectly flsht.

InthecascofFigs.8and-itheinclinededge a of the synthetic resin crystalhas been softened throughout its thickness by means of .a thermalprocess applied before the crystal was curved. By

7 this softening a pasty and resilient consistence has been given to thecrystal which is characteristic for such artificial resins and whichimparts to a watch crystal the qualification of an unsurpassed hermeticpacking.

In the caseof Pig. 5, the softened layerbhasbeenattachedtotheumrsurfaceofthe edge a. Besides this the sameconditions exist here for attaching and tight keeping as in the Figs. 1and 2.

What I claim is:

1. A watch crystal of resilient transparent synthetic resin havingedges, one surface of said edges comprising a permanently soft syntheticresin material.

2. A watch crystal of resilient transparent synthetic resin having edgesand a separate superposed layer of permanently soft synthetic resinmaterial on said ed!!!- 8. A watch crystal of resilient t syntheticresin havina integral edges consisting of-a soft synthetic resinmaterial.

ERNEST MORE.

